The present invention relates to the installation of an adhesive-backed printing blanket on a cylinder and, more particularly, a device and method for positioning the printing blanket on the cylinder so that it is wrapped evenly on the cylinder.
A printing blanket comprises an outer layer, formed mainly of a polymeric material, and a backing material on one side of the outer layer. The other side of the outer layer is the printing surface which carries ink for printing. The blanket is wrapped on a cylinder to transfer an inked image from a printing plate to paper during the printing process. To achieve high quality printing, the blanket must not slip or creep on the cylinder. One method of securing the blanket to the cylinder has been to lock the leading and trailing edges of the blanket in a spring-loaded mechanism housed in a gap or groove extending axially along the surface of the cylinder. Unfortunately, unsecured portions of the blanket may continue to slip and the locking mechanisms make installation and removal of the blanket cumbersome.
Another method of securing the blanket to the cylinder which has been used is to coat the back or nonprinting side of the printing blanket with a high tack adhesive. This method of installation of the blanket is less complicated and reduces blanket-creep on the cylinder by securing all portions of the blanket to the cylinder with adhesive. Such adhesive-backed blankets comprise a printing blanket having a pressure-sensitive adhesive coating on the backing material for securing the blanket to the cylinder and a release film, such as polyethylene, covering the adhesive coating. The release film serves as a protective covering to preserve the adhesive coating before the blanket is installed on the cylinder.
The blanket is installed on the cylinder by peeling back the protective covering about one inch from the leading edge across the entire width of the blanket and attaching the leading edge to the cylinder so that it is properly aligned with the edge of the gap and the side edges of the cylinder. Once the leading edge of the blanket is properly positioned on the cylinder, the cylinder is rotated slowly and the protective covering is removed as the cylinder rotates. As a result, the remaining portion of the blanket is attached and stuck to the cylinder as the cylinder rotates.
Although the adhesive-backed blanket simplified installation, it created a new set of problems related to the proper alignment of the adhesive-backed blanket on the cylinder. More specifically, it is difficult to axially align the leading edge of the blanket with the edge of the gap and the side edge of the cylinder. If the leading edge is not properly aligned, a wrinkle can form in the blanket or a pocket of air may be trapped resulting in a bubble as it is wrapped around the rotating cylinder. In any event, an improperly installed adhesive-backed blanket must be removed and properly reinstalled. Removal of the blanket, however, reduces the adhesiveness of the backing which negates one of the benefits of using the adhesive-backed blanket, i.e., reducing blanket-creep on the cylinder. Additionally, even though installation may be simplified, it is still cumbersome and time consuming.
Accordingly, there is a need for a device and method for facilitating the proper axial alignment of the leading edge of an adhesive-backed printing blanket on a cylinder and for holding the leading edge of the blanket in place to achieve the necessary dimensional stability for wrapping the blanket evenly around the cylinder.